has boundary has 2D boundary has 2D boundary RO:0002002 has_boundary uberon A 2D boundary may have holes and gaps, but it must be a single connected entity, not an aggregate of several disconnected parts. has_boundary Although the boundary is two-dimensional, it exists in three-dimensional space and thus has a 3D shape. a relation between a material entity and a 2D immaterial entity (the boundary), in which the boundary delimits the material entity has boundary has_2D_boundary my body has 2D boundary the surface of my skin mereotopologically related to material entity material entity immaterial entity axiom holds for all times